1. Field of the Invention
This invention relates to a thermoplastic elastomer composition, and formed article and composite formed article of the same; more particularly to a thermoplastic elastomer composition excellent in softness, permanent compression set (both short- and long-term) and moldability, and controlled in bleed-out of the softening agent, and a formed article and composite formed article of the same.
2. Description of the Prior Art
Recently, thermoplastic elastomers, which are soft materials with rubber elasticity, need no vulcanization, and are as moldable and recyclable as thermoplastic resins, have been widely used in various areas, such as automobile parts, home electric appliances, wire coatings, medical equipment parts, footwear and miscellaneous goods.
Of thermoplastic elastomers, polystyrene-based ones, e.g., styrene-butadiene block copolymer (SBS) and styrene-isoprene block copolymer (SIS) as aromatic vinyl compound and conjugated diene compound block copolymers, are highly soft, have good rubber elasticity at normal temperature and give highly moldable thermoplastic elastomer compositions. As such, they are widely used as substitutes for vulcanized rubber.
The elastomer composition of styrene and conjugated diene block copolymer, as one type of the above elastomers, whose intramolecular double bonds are hydrogenated, is more widely used as the one having improved resistance to aging under heat (thermal stability) and to weather.
However, the thermoplastic elastomer composition containing the hydrogenated block copolymer still has some problems regarding its rubber characteristics, e.g., resistance to oil, deformation rate (permanent compression set) and rubber elasticity at high temperature. The compositions containing a hydrogenated derivative of the above block copolymer have been crosslinked to improve the above characteristics, and these crosslinked compounds are disclosed, e.g., by Japanese Patent Laid-open Publication Nos.S59-6236 and S63-57662, and Japanese Patent Publication Nos.H3-49927, H3-11291 and H6-13628.
However, the crosslinked compositions of hydrogenated block copolymers disclosed by the above patent publications still have problems of insufficient permanent compression set at high temperature, in particular, at 100xc2x0 C., and of tending to lose mechanical strength. Therefore, they are still short of the performance level which has been required in the areas for vulcanized rubber, as matters now stand. Moreover, they involve many moldability-related problems, e.g., low melt tension of the extruded article at high temperature, deteriorating in its ability to keep its shape, and extended molding cycles of injection-molded articles.
Each of the compositions disclosed by the above patent publications has a Shore A hardness of 40 or more, and is softened by increasing their softening agent content. However, this causes practical problems, e.g., sticky surfaces of the molded article and bleed-out of the softening agent in the presence of stress under heating, as matters now stand.
It is an object of the present invention to provide a thermoplastic elastomer composition excellent in softness, permanent compression set (both short- and long-term) and resistance to oil, and controlled in bleed-out of the softening agent. It is another object of the present invention to provide. a formed article and composite formed article of the above thermoplastic elastomer composition.
The inventors of the present invention have found, after having extensively studied to achieve the above objects, that a thermoplastic elastomer composition excellent in softness, permanent compression set and moldability, and controlled in bleed-out of the softening agent can be obtained by melting and kneading a specific, hydrogenated block copolymer elastomer with a thermoplastic resin of low melting point and melt viscosity, thereby achieving the present invention.
The first aspect of the invention is a thermoplastic elastomer composition containing:
(a) 100 parts by weight of at least one hydrogenated block copolymer selected from the group consisting of:
(a-1) a hydrogenated block copolymer obtained by hydrogenating a block copolymer composed of at least 2 polymer blocks A mainly based on an aromatic vinyl compound and at least one polymer block B mainly based on a conjugated diene compound, and
(a-2) a hydrogenated block copolymer obtained by hydrogenating a block copolymer based on a conjugated diene compound;
(b) 30 to 150 parts by weight of a non-aromatic-based softening agent for rubber; and
(c) 3 to 100 parts by weight of a thermoplastic resin having a melting point of 70 to 140xc2x0 C., determined by DSC analysis, and a melt viscosity of 400 to 100,000 cps at 140xc2x0 C.
The second aspect of the invention is the thermoplastic elastomer composition of the first aspect, which further contains (d) 0.01 to 3 parts by weight of an organic peroxide.
The third aspect of the invention is the thermoplastic elastomer composition of the first or second aspects, wherein the thermoplastic resin as the component (c) is of at least one thermoplastic resin selected from the group consisting of non-polar resin and resin having a polar group.
The fourth aspect of the invention is the thermoplastic elastomer composition of the third aspect, wherein the non-polar resin is a polyethylene wax.
The fifth aspect of the invention is the thermoplastic elastomer composition of the third aspect, wherein the resin having a polar group is of at least one of the resins selected from the group consisting of ionomer, ethylene/acrylic acid copolymer, ethylene/vinyl acetate copolymer, saponified ethylene/vinyl acetate copolymer, polyamide-based resin, polyamide-based thermoplastic elastomer, biodegradable polyester-based resin, polyester-based resin, polyester-based thermoplastic elastomer, polyurethane-based resin and polyurethane-based thermoplastic elastomer.
The sixth aspect of the invention is the thermoplastic elastomer composition of the first or second aspects, which further contains (e) 0.1 to 5 parts by weight of liquid polybutadiene containing hydroxyl group at the terminal or derivative thereof, when the component (c) is a polar resin.
The seventh aspect of the invention is the thermoplastic elastomer composition of the first or second aspects, which further contains (f) 0.1 to 5 parts by weight of an unsaturated glycidyl compound or derivative thereof, when the component (c) is a polar resin.
The eighth aspect of the invention is the thermoplastic elastomer composition of the first or second aspects, which further contains (g) 0.1 to 5 parts by weight of an unsaturated carboxylic acid or derivative thereof, when the component (c) is a polar resin.
The ninth aspect of the invention is the thermoplastic elastomer composition of the first or second aspects, which further contains (h) 0.1 to 10 parts by weight of an ester-based crosslinking aid.
The tenth aspect of the invention is the thermoplastic elastomer composition of the first or second aspects, which further contains (i) 0.1 to 25 parts by weight of a peroxide-decomposed type polyolefin resin.
The eleventh aspect of the invention is a formed article composed of the thermoplastic elastomer composition of the first or second aspects.
The twelfth aspect of the invention is an elastic part composed of the formed article of the eleventh aspect for medical, food or bubble jet printer purpose.
The thirteen aspect of the invention is a thermal adhesiveness composite article composed of the formed article of the eleventh aspect and a formed article of polypropylene-based resin adhered to each other under heating.
The fourteenth aspect of the invention is an elastic part composed of the thermal adhesiveness formed article of the thirteenth aspect for medical, food or bubble jet printer purpose.